In vivo mammary ductal and alveolar cells rest on a basement membrane containing type IV collagen. The objective of this project was to study the role of basement membrane collagen in normal and neoplastic mammary growth. An in vitro system for the primary culture of normal mammary epithelium and DMBA induced mammary tumor cells was developed. We have shown that normal mammary epithelium in culture synthesizes basement membrane collagen and that process is under hormonal control. We will now demonstrate that normal mammary epithelium preferentially attaches to basement membrane collagen compared to stromal collagen. Attachment, spreading and growth of these cells on stromal collagen requires the synthesis of basement membrane collagen and can be blocked by the proline analog cis-hydroxyproline. Unlike normal epithelium mammary fibroblasts or tumor cells show no preferential attachment to any collagen type. Studies were begun to correlate these in vitro findings with the collagen requirements for growth of normal mammary epithelium and DMBA induced mammary tumors in vivo.